Rupturing or removing hydrogen atoms from a hydrogen-containing molecule is commonly referred to as hydrogen abstraction in chemistry. A number of reactants can be used in hydrogen abstraction. Common reactants include hydrogen atoms, halogen atoms, hydroxyl radicals, and other radical species. Although the reactants are reactive, an activation energy is still commonly required for hydrogen abstraction and some reactions thus require adequate thermal energy (A.A. Zavitsas, Journal of American Chemical Society 120(1998)6578-6586). Worst of all, most of these reactants, in addition to removing hydrogen atoms, also react with other chemical functional groups in the molecule and/or may remove non-hydrogen atoms. Further, some of these reactive species are toxic, environmentally harmful, or costly. Novel and economical reaction routes for selective hydrogen abstraction are thus desirable.
In the research and development of new reaction routes, scientists have discovered that the kinetic energy of a reactant can be an important reaction attribute. It can be used to drive a chemical reaction which otherwise relies totally on chemical potentials and thermal energy. The best fundamental evidence can be found in most scientific articles on molecular beam research in the literature (see for example, M. A. D. Fluendy and K. P. Lawley, “Chemical applications of molecular beam scattering”, Chapman and Hall, 1973). In this research, a beam of atoms or molecules having a specific kinetic energy and internal energy is directed to a target. The energy exchange and resultant chemical reactions are examined.
Normally, kinetic energy is added to the atoms or molecules when they are adiabatically expanded with an inert gas through a small nozzle. The velocity of the atoms or molecules can increase to supersonic speed. However, this technique is sometimes not suitable for light species, since the kinetic energy of a light atom like hydrogen traveling at supersonic speed is still much less than 0.1 eV.
The kinetic energies of the atoms or molecules can also be increased by ionizing them and then accelerating them using an electrostatic ion acceleration process. These accelerated ions can be used to bombard a target in an “ion bombardment” process. Many industrial processes use ion bombardment to reduce the reliance of synthetic reactions on thermal energy and to promote reactions via non-thermal equilibrium pathways (see for example, O. Auciello and R. Kelly, “Ion bombardment modification of surfaces”, Elsevier Science, 1984).
Ion bombardment processes have also been used in surface composition measurements, specifically in “direct recoiling” processes. Direct recoiling refers to the collision event in which a projectile, usually an accelerated ion, hits an atom on a solid surface and transfers some kinetic energy to the atom, causing the atom to depart from the surface directly. Since the late 70's, studies of direct recoiling have been developed into a practical surface science technique for the detection of light elements adsorbed on a solid surface.
In a typical direct recoiling process, inert gas ions at a few keV are used to recoil light atoms to an analysis detector (see for example, J. W. Rabalais, “Direct recoil spectrometry”, CRC Critical Reviews in Solid State and Materials Science 14(1988)319-376). Direct recoil spectrometry has been recognized as one of the few surface science techniques capable of detecting hydrogen on a solid surface containing hydrogen. For example, Rabalais and coworkers used 4 keV Ar+ to recoil hydrogen from CH3(CH2)16SH adsorbed on gold, CH3(CH2)15SH adsorbed on gold, and CF3(CH2)15SH adsorbed on gold (J. W. Rabalais and coworkers, Journal of Chemical Physics 109(1998)9134-9147), and 4 keV K+ to recoil hydrogen from C2H4 adsorbed on platinum (J. W. Rabalais, Surface Science 221(1989)299-316), for the detection of hydrogen and the measurement of other surface science data. However, when bombarding hydrocarbon molecules with ions under such conditions, signals showing the rupturing of carbon for all molecules and fluorine for CF3(CH2)15SH were detected. These signals were as intense as those corresponding to recoiling hydrogen. Hence, the ion bombardment processes described by Rabalais et al. showed that hydrogen, carbon and fluorine are all removed. The processes described by Rabalais et al. cannot be used to selectively rupture hydrogen from a molecule.